For a long time it was Adam Cole, but I ended up not outright hating him after his NXT run. That said while I generally don't mind his tag team work with Old man Fish and Roddy. I really don't care for Kyle O'Reilly. 
I say it every time I see him on TV - I hate Don Callis and it's nothing how he portrays his character. I just don't want this dude on my TV screen.
I don't know what this spells for the future on the main roster but NXT has several dudes that I just do not care for like Hank and Tank, Deaf Orton, Ridge Holland to name a few. 
On the women's side Candice LeRae and Bum Ass Indi (if she shows up on my TV I'm going to be hating).
Classic Wrestlers that I didn't care for:
The Rock N Roll Express, Greg Valentine, Brutus Beefcake, Big Bossman, and Duggan.